Field of the Invention
The present invention relates to a walking assist device which assists a user in walking.
Description of the Related Art
Conventionally, there has been known a walking assist device which assists a person (hereinafter, referred to as “user”) in walking who has difficulty in walking due to muscle weakness or the like (for example, refer to Japanese Patent Application Laid-Open No. 2007-000616).
This walking assist device includes a seating portion where the user sits, a pair of right and left leg links swingably connected to the seating portion, and two actuators provided in the leg links, respectively. The leg links each have a thigh frame, a crus frame, and a joint connecting these frames.
The walking assist device having the above configuration drives the joint connecting the frames by using the actuator to cause a force supporting a part of the weight of the user (hereinafter, referred to as “assist force”) to act on the trunk of the user from each leg link, thereby reducing the burden on the user's legs during walking to assist the user in walking.
The magnitude of the assist force acting on the user from each leg link is determined by distributing a target assist force necessary for assisting the user in walking according to a ratio between the right-leg side treading force and the left-leg side treading force of the user.
If the leg link is fixed to each user's leg as in the walking assist device described in Japanese Patent Application Laid-Open No. 2007-000616, however, a difference occurs in a bending/stretching state (a bending/stretching state variable) between the user's legs in a situation where the user ascends or descends a slope or stairs. Accordingly, if the assist forces are controlled only based on a ratio between the right-leg side treading force and the left-leg side treading force of the user, there has been a possibility that a force is applied to the user in a direction not intended by the user.
For example, as illustrated in FIG. 6, in the conventional walking assist device, the magnitude of an assist force Fu1r from the right-leg side leg link 2 is the same as the magnitude of the assist force Fu1l from the left-leg side leg link 2 if the right and left treading forces of a user P are the same as each other when the user P is in an ascending walking state (for example, a state where the user P is ascending stairs or an uphill). As a result, a resultant force Fu1 between the two assist forces Fu1r and Fu1l gets into a force having not only a vertical component, but also a component directed backward of the user in the back-and-forth direction and therefore a force could be applied to the user P as if the user were pulled backward.
Meanwhile, as illustrated in FIG. 7, in the conventional walking assist device, the magnitude of an assist force Fd1r from the right-leg side leg link 2 is the same as the magnitude of the assist force Fd1l from the left-leg side leg link 2 if the right and left treading forces of the user P are the same as each other when the user P is in a descending walking state (for example, a state where the user P is descending stairs or a downhill). As a result, a resultant force Fd1 between the two assist forces Fd1r and Fd1l gets into a force having not only a vertical component, but also a component directed forward of the user in the back-and-forth direction and therefore a force could be applied to the user P as if the user were pulled forward.